As the feature size of a metal oxide semiconductor (MOS) transistor has been reduced, the length of a gate and the length of a channel formed therebelow are also gradually decreasing. Accordingly, various studies are under way to increase capacitance between the gate and the channel and to improve operating characteristics of the MOS transistor.
As a thickness of a silicon oxide film mainly used as a gate insulating film is gradually reduced, the silicon oxide film may experience physical limitations in its electrical property. Therefore, in order to replace the conventional silicon oxide film, research into a high-k film having a high dielectric constant is actively being conducted. The high-k film may reduce leakage current between a gate electrode and a channel region while maintaining a small thickness of an equivalent oxide film.
Polysilicon mainly used as a gate material may have higher resistance than most metals. Accordingly, the current tendency is to replace the polysilicon gate electrode with a metal gate electrode.